Tutorial de como se coloca estrela caindo do mouse. 

Primeiro você deve salvar uma cópia de todo o seu theme no seu computador, caso queira voltá-lo ao que era antes.

Depois você entra em “Customize > Theme”, e cola o seguinte código antes de </body>:


<script type='text/javascript'>

// <![CDATA[

var colour="COR DA ESTRELA";

var sparkles=50;

var x=ox=400;

var y=oy=300;

var swide=800;

var shigh=600;

var sleft=sdown=0;

var tiny=new Array();

var star=new Array();

var starv=new Array();

var starx=new Array();

var stary=new Array();

var tinyx=new Array();

var tinyy=new Array();

var tinyv=new Array();

window.onload=function() { if (document.getElementById) {

  var i, rats, rlef, rdow;

  for (var i=0; i<sparkles; i++) {

    var rats=createDiv(3, 3);

    rats.style.visibility="hidden";

    document.body.appendChild(tiny[i]=rats);

    starv[i]=0;

    tinyv[i]=0;

    var rats=createDiv(5, 5);

    rats.style.backgroundColor="transparent";

    rats.style.visibility="hidden";

    var rlef=createDiv(1, 5);

    var rdow=createDiv(5, 1);

    rats.appendChild(rlef);

    rats.appendChild(rdow);

    rlef.style.top="2px";

    rlef.style.left="0px";

    rdow.style.top="0px";

    rdow.style.left="2px";

    document.body.appendChild(star[i]=rats);

  }

  set_width();

  sparkle();

}}

function sparkle() {

  var c;

  if (x!=ox || y!=oy) {

    ox=x;

    oy=y;

    for (c=0; c<sparkles; c++) if (!starv[c]) {

      star[c].style.left=(starx[c]=x)+"px";

      star[c].style.top=(stary[c]=y)+"px";

      star[c].style.clip="rect(0px, 5px, 5px, 0px)";

      star[c].style.visibility="visible";

      starv[c]=50;

      break;

    }

  }

  for (c=0; c<sparkles; c++) {

    if (starv[c]) update_star(c);

    if (tinyv[c]) update_tiny(c);

  }

  setTimeout("sparkle()", 40);

}

function update_star(i) {

  if (--starv[i]==25) star[i].style.clip="rect(1px, 4px, 4px, 1px)";

  if (starv[i]) {

    stary[i]+=1+Math.random()*3;

    if (stary[i]<shigh+sdown) {

      star[i].style.top=stary[i]+"px";

      starx[i]+=(i%5-2)/5;

      star[i].style.left=starx[i]+"px";

    }

    else {

      star[i].style.visibility="hidden";

      starv[i]=0;

      return;

    }

  }

  else {

    tinyv[i]=50;

    tiny[i].style.top=(tinyy[i]=stary[i])+"px";

    tiny[i].style.left=(tinyx[i]=starx[i])+"px";

    tiny[i].style.width="2px";

    tiny[i].style.height="2px";

    star[i].style.visibility="hidden";

    tiny[i].style.visibility="visible"

  }

}

function update_tiny(i) {

  if (--tinyv[i]==25) {

    tiny[i].style.width="1px";

    tiny[i].style.height="1px";

  }

  if (tinyv[i]) {

    tinyy[i]+=1+Math.random()*3;

    if (tinyy[i]<shigh+sdown) {

      tiny[i].style.top=tinyy[i]+"px";

      tinyx[i]+=(i%5-2)/5;

      tiny[i].style.left=tinyx[i]+"px";

    }

    else {

      tiny[i].style.visibility="hidden";

      tinyv[i]=0;

      return;

    }

  }

  else tiny[i].style.visibility="hidden";

}

document.onmousemove=mouse;

function mouse(e) {

  set_scroll();

  y=(e)?e.pageY:event.y+sdown;

  x=(e)?e.pageX:event.x+sleft;

}

function set_scroll() {

  if (typeof(self.pageYOffset)=="number") {

    sdown=self.pageYOffset;

    sleft=self.pageXOffset;

  }

  else if (document.body.scrollTop || document.body.scrollLeft) {

    sdown=document.body.scrollTop;

    sleft=document.body.scrollLeft;

  }

  else if (document.documentElement && (document.documentElement.scrollTop || document.documentElement.scrollLeft)) {

    sleft=document.documentElement.scrollLeft;

    sdown=document.documentElement.scrollTop;

  }

  else {

    sdown=0;

    sleft=0;

  }

}

window.onresize=set_width;

function set_width() {

  if (typeof(self.innerWidth)=="number") {

    swide=self.innerWidth;

    shigh=self.innerHeight;

  }

  else if (document.documentElement && document.documentElement.clientWidth) {

    swide=document.documentElement.clientWidth;

    shigh=document.documentElement.clientHeight;

  }

  else if (document.body.clientWidth) {

    swide=document.body.clientWidth;

    shigh=document.body.clientHeight;

  }

}

function createDiv(height, width) {

  var div=document.createElement("div");

  div.style.position="absolute";

  div.style.height=height+"px";

  div.style.width=width+"px";

  div.style.overflow="hidden";

  div.style.backgroundColor=colour;

  return (div);

}

// ]]>

</script>
Depois é só substituir o código da cor da estrela.